The present invention relates to inspection performed in a manufacturing process of hard disk media and more particularly to a technique for detecting the shapes of patterns formed on a patterned medium and thereby to detect defectively shaped patterns.
In recent years, the application of hard disk drives to severs and computers has been increasing; at the same time, the application of them has been extending to other purposes such as home-use hard disk recorders, car navigation systems, and portable audio-visual reproducing devices. The capacity of hard disk drives has also been increasing with the digitalization of various devices.
Increasing the capacity of a hard disk drive means increasing the recording density of a medium disk. As one of the technologies for increasing the recording density of a medium disk, a patterned medium is expected to be introduced in the future. As shown in FIG. 2, there are two kinds of patterned media: a discrete track medium, and a bit patterned medium. The discrete track medium is based on a method in which a concentric circular track pattern 14 is formed on the medium disk 10 as shown on the left side of FIG. 2. The bit patterned medium is based on a method in which an infinite number of bit patterns 16 are formed as shown on the right side of FIG. 2.
Heretofore, a magnetic film is formed on a surface of a disk; and the magnetic film is then divided into in areas, each of which corresponds to one bit. Data is recorded by magnetizing each of the areas. In contrast, when a patterned medium is used, a magnetic material is used to form pattern elements on a surface of a disk as described above. Magnetic information is recorded to the formed pattern elements. Adjacent pattern elements are spaced apart from each other so that they are magnetically insulated from each other. This makes it possible to increase the recording density in comparison with the conventional continuous film medium that is provided with no space.
Nanoimprint technique is used for the formation of a pattern, which is a prevailing method. As shown in FIG. 3A, the nanoimprint technique uses a mold 20 through which a light beam passes, and a photoresist 22 that is applied to a surface of a disk substrate 12 on which a magnetic film is formed. A light beam passes through the mold 20. According to the nanoimprint technique, the mold 20 is pressed against the photoresist 22 applied to the surface of the disk substrate 12 (FIG. 3B); while this state is kept, the photoresist 22 is exposed to a light beam (FIG. 3C); after the mold 20 is removed (FIG. 3D), etching is performed (FIG. 3E); and consequently, a bit pattern is formed (FIG. 3F). In this case, if the mold 20 in itself is defective, or if a foreign particle adheres to the mold 20, a defect will also occur in a transferred pattern. Therefore, the introduction of the nanoimprint technique requires the execution of new inspection as to whether or not a bit pattern is properly formed.
Heretofore, as an inspection method for detecting a defect on a surface of a continuous film disk, there is a method described in JP-A-2000-180376. This method includes the steps of: irradiating a surface of a disk with a laser light beam; properly selecting a signal obtained from a light receiving element for detecting both a regular reflected light beam from the surface of the disk and scattered light; and performing processing corresponding to the signal so as to correctly identify a kind of defect. In particular, discrimination between a linear defect and a planar defect, or discrimination between a concave defect and a convex defect, can be correctly performed.
The defect inspection described in JP-A-2000-180376 is intended to discriminate between a linear defect and a planar defect, or between a concave defect and a convex defect, on a surface of a continuous film disk. The defect inspection in question does not make a judgment as to whether or not a bit pattern is properly formed on a patterned medium.
As a method for inspecting a minute pattern element whose size is several tens of nanometers, the use of SEM and AFM can be considered. However, when a SEM (scanning electron microscope) is used, only a shape of a pattern element formed on a surface, which is viewed from the top, can be inspected. If a cross-sectional shape of the pattern element is inspected, the pattern element must be broken. On the other hand, when an AFM (atom force microscope) is used, a three dimensional shape of a target pattern element can be measured. However, the measurement result varies depending on a state of a probe. Accordingly, there is a case where a shape of a pattern element cannot be correctly measured. In addition, from the viewpoint of throughput, 100-percent product inspection cannot be carried out by these methods. Moreover, only a limited area on a disk can be inspected.
If the inspection is intended for the nanoimprint process control, it is necessary to measure a correct shape of each pattern element. In contrast, if the inspection is intended for the quality control of products, it is necessary to inspect the whole surface of the disk on a 100-percent product basis. The above methods cannot satisfy these requirements.